Studies on the regulation of methionine biosynthesis in E. coli K12 will continue with emphasis on in vitro expression of selected met structural genes. Attempts to demonstrate in vitro repression of the genes will include preparation of different types of cell extracts which may contain active repressor, and experiments at the level of transcription under different ionic conditions than those used in a coupled system. We will also attempt to identify the metJ gene product as a band on polyacrylamide gel electrophoresis, and if successful will purify the metJ protein. To facilitate these experiments we will construct new transducing phage with less bacterial DNA by the use of recombinant DNA technology. The structures of the new phage and those already available will be studied by restriction fragment mapping and electron microscopy.